Delay lines are important components in many microwave and radio frequency (RF) circuits. They provide fixed delays and phase shifts that can perform a variety of signal processing functions. For example, delay lines are used in feed forward amplifiers to provide phase shifts effective to cancel large distortion products.
Typical transmission delay lines comprise lengths of coaxial cable or stripline transmission lines (“striplines”). For compactness, coaxial cable delay lines are helically coiled and striplines are formed in a meandering configuration. Coiled coaxial delay lines are reliable and low loss. However they are large, expensive and difficult to attach to conventional electronic circuit boards. Meandered striplines are inexpensive and easy to construct and connect, but they have relatively high loss, and the many bends associated with their meandering paths create unwanted reflections and delay distortion. Accordingly there is a need for an improved compact delay lines.